U.S. patent number 10,125,424 [Application Number 14/424,898] was granted by the patent office on 2018-11-13 for zirconium pretreatment compositions containing molybdenum, associated methods for treating metal substrates, and related coated metal substrates.
This patent grant is currently assigned to PPG Industries Ohio, Inc.. The grantee listed for this patent is PPG Industries Ohio, Inc.. Invention is credited to Philippe Maintier, Michel Sudour, Aline Wozniak.
United States Patent |
10,125,424 |
Sudour , et al. |
November 13, 2018 |
Zirconium pretreatment compositions containing molybdenum,
associated methods for treating metal substrates, and related
coated metal substrates
Abstract
Disclosed are pretreatment compositions and associated methods
for treating metal substrates with pretreatment compositions,
including ferrous substrates, such as cold rolled steel and
electrogalvanized steel. The pretreatment composition includes: a
Group IIIB and/or IVB metal; free fluoride; and molybdenum. The
methods include contacting the metal substrates with the
pretreatment composition.
Inventors: |
Sudour; Michel (Sebourg,
FR), Wozniak; Aline (Marly, FR), Maintier;
Philippe (Jenlain, FR) |
Applicant: |
Name |
City |
State |
Country |
Type |
PPG Industries Ohio, Inc. |
Cleveland |
OH |
US |
|
|
Assignee: |
PPG Industries Ohio, Inc.
(Cleveland, OH)
|
Family
ID: |
47294985 |
Appl.
No.: |
14/424,898 |
Filed: |
August 16, 2013 |
PCT
Filed: |
August 16, 2013 |
PCT No.: |
PCT/US2013/055354 |
371(c)(1),(2),(4) Date: |
February 27, 2015 |
PCT
Pub. No.: |
WO2014/035691 |
PCT
Pub. Date: |
March 06, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150225855 A1 |
Aug 13, 2015 |
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Foreign Application Priority Data
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Aug 29, 2012 [FR] |
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12 58080 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C
22/34 (20130101); C25D 13/02 (20130101); C25D
13/00 (20130101); C23C 22/44 (20130101); C25D
13/20 (20130101); C23C 22/83 (20130101); Y10T
428/12812 (20150115) |
Current International
Class: |
C23C
22/44 (20060101); C25D 13/02 (20060101); C25D
13/00 (20060101); C23C 22/83 (20060101); C23C
22/34 (20060101); C25D 13/20 (20060101) |
Field of
Search: |
;106/1.05 |
References Cited
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|
Primary Examiner: Klemanski; Helene
Attorney, Agent or Firm: Passerin, Esq.; Alicia M.
Claims
What is claimed is:
1. A pretreatment composition for treating a metal substrate
comprising: a Group IIIB and/or Group IVB metal; free fluoride;
molybdenum; and lithium; wherein the pH of the pretreatment
composition is 1 to 6.
2. The pretreatment composition of claim 1, wherein the Group IIIB
and/or Group IVB metal comprises zirconium.
3. The pretreatment composition of claim 1, wherein the molybdenum
is provided in the form of a salt.
4. The pretreatment composition of claim 3, wherein the salt
comprises sodium molybdate, calcium molybdate, potassium molybdate,
ammonium molybdate, molybdenum chloride, or molybdenum acetate,
molybdenum acetate, molybdenum sulfamate, molybdenum formate, or
molybdenum lactate.
5. The pretreatment composition of claim 1, wherein the lithium is
provided in the form of a salt.
6. The pretreatment composition of claim 5, wherein the salt
comprises lithium nitrate, lithium sulfate, lithium fluoride,
lithium chloride, lithium hydroxide, lithium carbonate, or lithium
iodide.
7. The pretreatment composition of claim 1, wherein the free
fluoride is present in an amount of 5 ppm to 250 ppm based on a
total weight of the ingredients in the pretreatment
composition.
8. The pretreatment composition of claim 1, wherein the molar ratio
of the Group IIIB and/or IVB metal is between 100:1 and 1:10.
9. The pretreatment composition of claim 1, further comprising a
resinous binder.
10. The pretreatment composition of claim 9, wherein the resinous
binder is water soluble and/or dispersible.
11. The pretreatment composition of claim 9, wherein the resinous
binder comprises a reaction product of one or more alkanolamines
and an epoxy-functional material containing at least two epoxy
groups, beta hydroxy ester, imide or sulfide functionality,
polyamides, or combinations thereof.
12. The pretreatment composition of claim 1, further comprising an
amine.
13. The pretreatment composition of claim 12, wherein the amine
comprises trimethylamine, methylethyl amine, or mixtures
thereof.
14. A pretreated metal substrate comprising a surface layer formed
from the composition of claim 1.
15. An electrophoretically coated metal substrate comprising: a
treated surface layer formed from the composition of claim 1; and
an electrophoretically deposited coating composition over at least
a portion of the treated surface layer, wherein the coating
composition comprises yttrium.
Description
FIELD OF THE INVENTION
The present invention relates to pretreatment compositions and
methods for treating a metal substrate, including ferrous
substrates such as cold rolled steel and electrogalvanized steel,
or aluminum alloys. The present invention also relates to a coated
metal substrate.
BACKGROUND OF THE INVENTION
The use of protective coatings on metal substrates for improved
corrosion resistance and paint adhesion is common. Conventional
techniques for coating such substrates include techniques that
involve pretreating the metal substrate with a phosphate conversion
coating and chrome-containing rinses. The use of such phosphate
and/or chromate-containing compositions, however, imparts
environmental and health concerns.
As a result, chromate-free and/or phosphate-free pretreatment
compositions have been developed. Such compositions are generally
based on chemical mixtures that react with the substrate surface
and bind to it to form a protective layer. For example,
pretreatment compositions based on a Group IIIB or IVB metal
compound have recently become more prevalent. Such compositions
often contain a source of free fluorine, i.e., fluorine that is
isolated in the pretreatment composition as opposed to fluorine
that is bound to another element, such as the Group IIIB or IVB
metal. Free fluorine can etch the surface of the metal substrate,
thereby promoting deposition of a Group IIIB or IVB metal coating.
Nevertheless, the corrosion resistance capability of these
pretreatment compositions has generally been significantly inferior
to conventional phosphate and/or chromium containing
pretreatments.
It would be desirable to provide methods for treating a metal
substrate that overcome at least some of the previously described
drawbacks of the prior art, including the environmental drawbacks
associated with the use of chromates and/or phosphates. It also
would be desirable to provide methods for treating metal substrate
that imparts corrosion resistance properties that are equivalent
to, or even superior to, the corrosion resistance properties
imparted through the use of phosphate conversion coatings. It would
also be desirable to provide related coated metal substrates.
SUMMARY OF THE INVENTION
In certain respects, the present invention is directed to a method
of coating a metal substrate comprising: pretreating the metal
substrate with a pretreatment composition comprising a Group IIIB
and/or Group IVB metal, free fluoride, and molybdenum; and
electrophoretically depositing a coating composition onto the metal
substrate, wherein the coating composition comprises yttrium.
In still other respects, the present invention is directed to a
method of coating a metal substrate comprising electrophoretically
depositing a coating composition onto the metal substrate, wherein
the coating composition comprises yttrium, and wherein the metal
substrate comprises a treated surface layer comprising a Group IVB
metal, free fluoride, and molybdenum.
In still other respects, the present invention is directed to a
pretreatment composition for treating a metal substrate comprising
a Group IIIB and/or Group IVB metal, free fluoride, molybdenum, and
lithium.
In still other respects, the present invention is directed to a
pretreated metal substrate comprising a surface layer comprising a
Group IIIB and/or Group IVB metal, free fluoride, molybdenum, and
lithium on at least a portion of the substrate.
In still other respects, the present invention is directed to an
electrophoretically coated metal substrate comprising a treated
surface layer comprising a Group IIIB and/or Group IVB metal, free
fluoride, and molybdenum on a surface of the metal substrate, and
an electrophoretically deposited coating composition over at least
a portion of the treated surface layer, wherein the coating
composition comprises yttrium.
DETAILED DESCRIPTION
For purposes of the following detailed description, it is to be
understood that the invention may assume various alternative
variations and step sequences, except where expressly specified to
the contrary. Moreover, other than in any operating examples, or
where otherwise indicated, all numbers expressing, for example,
quantities of ingredients used in the specification and claims are
to be understood as being modified in all instances by the term
"about". Accordingly, unless indicated to the contrary, the
numerical parameters set forth in the following specification and
attached claims are approximations that may vary depending upon the
desired properties to be obtained by the present invention. At the
very least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of the claims, each numerical
parameter should at least be construed in light of the number of
reported significant digits and by applying ordinary rounding
techniques.
Notwithstanding that the numerical ranges and parameters setting
forth the broad scope of the invention are approximations, the
numerical values set forth in the specific examples are reported as
precisely as possible. Any numerical value, however, inherently
contains certain errors necessarily resulting from the standard
variation found in their respective testing measurements.
Also, it should be understood that any numerical range recited
herein is intended to include all sub-ranges subsumed therein. For
example, a range of "1 to 10" is intended to include all sub-ranges
between (and including) the recited minimum value of 1 and the
recited maximum value of 10, that is, having a minimum value equal
to or greater than 1 and a maximum value of equal to or less than
10.
In this application, the use of the singular includes the plural
and plural encompasses singular, unless specifically stated
otherwise. In addition, in this application, the use of "or" means
"and/or" unless specifically stated otherwise, even though "and/or"
may be explicitly used in certain instances.
Unless otherwise disclosed herein, as used herein, the term
"substantially free" means that a particular material is not
purposefully added to a composition and only is present in trace
amounts or as an impurity. As used herein, the term "completely
free" means that a composition does not comprise a particular
material. That is, the composition comprises 0 weight percent of
such material.
Certain embodiments of the present invention provide a method of
coating a metal substrate comprising pretreating the metal
substrate with a pretreatment composition comprising a Group IIIB
and/or Group IVB metal, free fluoride, and molybdenum, and
electrophoretically depositing a coating composition onto the metal
substrate, wherein the coating composition comprises yttrium.
Certain embodiments of the pretreatment composition are directed to
a pretreatment composition for treating a metal substrate
comprising a Group IIIB and/or Group IVB metal, free fluoride, and
molybdenum. Lithium may also be included in the pretreatment
composition. In certain embodiments, the pretreatment composition
may be substantially free of phosphates and/or chromates. The
treatment of the metal substrate with the pretreatment composition
results in good corrosion resistance properties. Inclusion of
molybdenum in and/or molybdenum in combination with lithium in the
pretreatment composition may provide improved corrosion performance
on steel and steel substrates.
Certain embodiments of the present invention are directed to
compositions and methods for treating a metal substrate. Suitable
metal substrates for use in the present invention include those
that are often used in the assembly of automotive bodies,
automotive parts, and other articles, such as small metal parts,
including fasteners, i.e., nuts, bolts, screws, pins, nails, clips,
buttons, and the like. Specific examples of suitable metal
substrates include, but are not limited to, cold rolled steel, hot
rolled steel, steel coated with zinc metal, zinc compounds, or zinc
alloys, such as electrogalvanized steel, hot-dipped galvanized
steel, galvanealed steel, and steel plated with zinc alloy. Also,
aluminum alloys, aluminum plated steel and aluminum alloy plated
steel substrates may be used. Other suitable non-ferrous metals
include copper and magnesium, as well as alloys of these materials.
Moreover, the metal substrate being treated by the methods of the
present invention may be a cut edge of a substrate that is
otherwise treated and/or coated over the rest of its surface. The
metal substrate treated in accordance with the methods of the
present invention may be in the form of, for example, a sheet of
metal or a fabricated part.
The substrate to be treated in accordance with the methods of the
present invention may first be cleaned to remove grease, dirt, or
other extraneous matter. This is often done by employing mild or
strong alkaline cleaners, such as are commercially available and
conventionally used in metal pretreatment processes. Examples of
alkaline cleaners suitable for use in the present invention include
Chemkleen 163, Chemkleen 166M/C, Chemkleen 490MX, Chemkleen 2010LP,
Chemkleen 166 HP, Chemkleen 166 M, Chemkleen 166 M/Chemkleen
171/11, each of which are commercially available from PPG
Industries, Inc. Such cleaners are often followed and/or preceded
by a water rinse.
In certain embodiments, prior to the pretreatment step, the
substrate may be contacted with a pre-rinse solution. Pre-rinse
solutions, in general, may utilize certain solubilized metal ions
or other inorganic materials (such as phosphates or simple or
complex fluorides or acids) to enhance the corrosion protection of
pretreated metal substrates. Suitable non-chrome pre-rinse
solutions that may be utilized in the present invention are
disclosed in U.S. Patent Application 2010/0159258A1 assigned to PPG
Industries, Inc. and herein incorporated by reference.
Certain embodiments of the present invention are directed to
methods for treating a metal substrate, with or without the
optional pre-rinse, that comprise contacting the metal substrate
with a pretreatment composition comprising a Group IIIB and/or IVB
metal. As used herein, the term "pretreatment composition" refers
to a composition that, upon contact with the substrate, reacts with
and chemically alters the substrate surface and binds to it to form
a protective layer.
The pretreatment composition may comprise a carrier, often an
aqueous medium, so that the composition is in the form of a
solution or dispersion of a Group IIIB or IVB metal compound in the
carrier. In these embodiments, the solution or dispersion may be
brought into contact with the substrate by any of a variety of
known techniques, such as dipping or immersion, spraying,
intermittent spraying, dipping followed by spraying, spraying
followed by dipping, brushing, or roll-coating. In certain
embodiments, the solution or dispersion when applied to the metal
substrate is at a temperature ranging from 60 to 185.degree. F. (15
to 85.degree. C.). For example, the pretreatment process may be
carried out at ambient or room temperature. The contact time is
often from 10 seconds to 5 minutes, such as 30 seconds to 2
minutes.
As used herein, the term "Group IIIB and/or IVB metal" refers to an
element that is in Group IIIB or Group IVB of the CAS Periodic
Table of the Elements. Where applicable, the metal themselves may
be used. In certain embodiments, a Group IIIB and/or Group IVB
metal compounds is used. As used herein, the term "Group IIIB
and/or IVB metal compound" refers to compounds that include at
least one element that is in Group IIIB or Group IVB of the CAS
Period Table of the Elements.
In certain embodiments, the Group IIIB and/or IVB metal compound
used in the pretreatment composition is a compound of zirconium,
titanium, hafnium, yttrium, cerium, or a mixture thereof. Suitable
compounds of zirconium include, but are not limited to,
hexafluorozirconic acid, alkali metal and ammonium salts thereof,
ammonium zirconium carbonate, zirconyl nitrate, zirconyl sulfate,
zirconium carboxylates and zirconium hydroxy carboxylates, such as
hydrofluorozirconic acid, zirconium acetate, zirconium oxalate,
ammonium zirconium glycolate, ammonium zirconium lactate, ammonium
zirconium citrate, and mixtures thereof. Suitable compounds of
titanium include, but are not limited to, fluorotitanic acid and
its salts. A suitable compound of hafnium includes, but is not
limited to, hafnium nitrate. A suitable compound of yttrium
includes, but is not limited to, yttrium nitrate. A suitable
compound of cerium includes, but is not limited to, cerous
nitrate.
In certain embodiments, the Group IIIB and/or IVB metal is present
in the pretreatment composition in an amount of 50 to 500 parts per
million ("ppm") metal, such as 75 to 250 ppm, based on the total
weight of all of the ingredients in the pretreatment composition.
The amount of Group IIIB and/or IVB metal in the pretreatment
composition can range between the recited values inclusive of the
recited values.
The pretreatment compositions also comprise free fluoride. The
source of free fluoride in the pretreatment compositions of the
present invention can vary. For example, in some cases, the free
fluoride may derive from the Group IIIB and/or IVB metal compound
used in the pretreatment composition, such as is the case, for
example, with hexafluorozirconic acid. As the Group IIIB and/or IVB
metal is deposited upon the metal substrate during the pretreatment
process, fluorine in the hexafluorozirconic acid will become free
fluoride and the level of free fluoride in the pretreatment
composition will, if left unchecked, increase with time as metal is
pretreated with the pretreatment composition of the present
invention.
In addition, the source of free fluoride in the pretreatment
compositions of the present invention may include a compound other
than the Group IIIB and/or IVB metal compound. Non-limiting
examples of such sources include HF, NH.sub.4F, NH.sub.4HF.sub.2,
NaF, and NaHF.sub.2. As used herein, the term "free fluoride"
refers to isolated fluoride ions.
In certain embodiments, the free fluoride is present in the
pretreatment composition in an amount of 5 to 250 ppm, such as 25
to 150 ppm, based on the total weight of the ingredients in the
pretreatment composition. The amount of free fluoride in the
pretreatment composition can range between the recited values
inclusive of the recited values.
In certain embodiments, a K ratio of a compound (A) containing a
Group IIIB and/or Group IVB metal in mole weight to a compound (B)
containing fluorine as a supplying source of free fluoride in mole
weight calculated as HF has a ratio of K=A/B, where K>0.10. In
certain embodiments, 0.11<K<0.25.
The pretreatment compositions also comprise molybdenum. In certain
embodiments, the source of molybdenum used in the pretreatment
composition is in the form of a salt. Suitable molybdenum salts are
sodium molybdate, calcium molybdate, potassium molybdate, ammonium
molybdate, molybdenum chloride, molybdenum acetate, molybdenum
sulfamate, molybdenum formate, or molybdenum lactate. In certain
embodiments, the inclusion of molybdenum in the pretreatment
composition results in improved corrosion resistance of steel and
steel substrates.
In certain embodiments, the molybdenum is present in the
pretreatment composition in an amount of 5 to 500 ppm, such as 5 to
150 ppm, based on the total weight of the ingredients in the
pretreatment composition. The amount of molybdenum in the
pretreatment composition can range between the recited values
inclusive of the recited values.
In certain embodiments, the molar ratio of the Group IIIB and/or
IVB metal to the molybdenum is between 100:1 and 1:10, for example,
between 30:1 and 11.
In certain embodiments, the pretreatment compositions also comprise
an electropositive metal. As used herein, the term "electropositive
metal" refers to metals that are more electropositive than the
metal substrate. This means that, for purposes of the present
invention, the term "electropositive metal" encompasses metals that
are less easily oxidized than the metal of the metal substrate that
is being treated. As will be appreciated by those skilled in the
art, the tendency of a metal to be oxidized is called the oxidation
potential, is expressed in volts, and is measured relative to a
standard hydrogen electrode, which is arbitrarily assigned an
oxidation potential of zero. The oxidation potential for several
elements is set forth in Table 1 below. An element is less easily
oxidized than another element if it has a voltage value, E*, in the
following table, that is greater than the element to which it is
being compared.
TABLE-US-00001 TABLE 1 Element Half-cell reaction Voltage, E*
Potassium K.sup.+ + e .fwdarw. K -2.93 Calcium Ca.sup.2+ + 2e
.fwdarw. Ca -2.87 Sodium Na.sup.+ + e .fwdarw. Na -2.71 Magnesium
Mg.sup.2+ + 2e .fwdarw. Mg -2.37 Aluminum Al.sup.3+ + 3e .fwdarw.
Al -1.66 Zinc Zn.sup.2+ + 2e .fwdarw. Zn -0.76 Iron Fe.sup.2+ + 2e
.fwdarw. Fe -0.44 Nickel Ni.sup.2+ + 2e .fwdarw. Ni -0.25 Tin
Sn.sup.2+ + 2e .fwdarw. Sn -0.14 Lead Pb.sup.2+ + 2e .fwdarw. Pb
-0.13 Hydrogen 2H.sup.+ + 2e .fwdarw. H.sub.2 -0.00 Copper
Cu.sup.2+ + 2e .fwdarw. Cu 0.34 Mercury Hg.sub.2.sup.2+ + 2e
.fwdarw. 2Hg 0.79 Silver Ag.sup.+ + e .fwdarw. Ag 0.80 Gold
Au.sup.3+ + 3e .fwdarw. Au 1.50
Thus, as will be apparent, when the metal substrate comprises one
of the materials listed earlier, such as cold rolled steel, hot
rolled steel, steel coated with zinc metal, zinc compounds, or zinc
alloys, hot-dipped galvanized steel, galvanealed steel, steel
plated with zinc alloy, aluminum alloys, aluminum plated steel,
aluminum alloy plated steel, magnesium and magnesium alloys,
suitable electropositive metals for deposition thereon include, for
example, nickel, copper, silver, and gold, as well mixtures
thereof.
In certain embodiments in which the electropositive metal comprises
copper, both soluble and insoluble compounds may serve as the
source of copper in the pretreatment compositions. For example, the
supplying source of copper ions in the pretreatment composition may
be a water soluble copper compound. Specific examples of such
materials include, but are not limited to, copper cyanide, copper
potassium cyanide, copper sulfate, copper nitrate, copper
pyrophosphate, copper thiocyanate, disodium copper
ethylenediaminetetraacetate tetrahydrate, copper bromide, copper
oxide, copper hydroxide, copper chloride, copper fluoride, copper
gluconate, copper citrate, copper lauroyl sarcosinate, copper
formate, copper acetate, copper propionate, copper butyrate, copper
lactate, copper oxalate, copper phytate, copper tartarate, copper
malate, copper succinate, copper malonate, copper maleate, copper
benzoate, copper salicylate, copper aspartate, copper glutamate,
copper fumarate, copper glycerophosphate, sodium copper
chlorophyllin, copper fluorosilicate, copper fluoroborate and
copper iodate, as well as copper salts of carboxylic acids in the
homologous series formic acid to decanoic acid, copper salts of
polybasic acids in the series oxalic acid to suberic acid, and
copper salts of hydroxycarboxylic acids, including glycolic,
lactic, tartaric, malic and citric acids.
When copper ions supplied from such a water-soluble copper compound
are precipitated as an impurity in the form of copper sulfate,
copper oxide, etc., it may be desirable to add a complexing agent
that suppresses the precipitation of copper ions, thus stabilizing
them as a copper complex in the solution.
In certain embodiments, the copper compound is added as a copper
complex salt such as K.sub.3Cu(CN).sub.4 or Cu-EDTA, which can be
present stably in the pretreatment composition on its own, but it
is also possible to form a copper complex that can be present
stably in the pretreatment composition by combining a complexing
agent with a compound that is difficulty soluble on its own.
Examples thereof include a copper cyanide complex formed by a
combination of CuCN and KCN or a combination of CuSCN and KSCN or
KCN, and a Cu-EDTA complex formed by a combination of CuSO.sub.4
and EDTA.2Na.
With regard to the complexing agent, a compound that can form a
complex with copper ions can be used; examples thereof include
inorganic compounds such as cyanide compounds and thiocyanate
compounds, and polycarboxylic acids, and specific examples thereof
include ethylenediaminetetraacetic acid, salts of
ethylenediaminetetraacetic acid such as dihydrogen disodium
ethylenediaminetetraacetate dihydrate, aminocarboxylic acids such
as nitrilotriacetic acid and iminodiacetic acid, oxycarboxylic
acids such as citric acid and tartaric acid, succinic acid, oxalic
acid, ethylenediaminetetramethylenephosphonic acid, and
glycine.
In certain embodiments, the electropositive metal is present in the
pretreatment composition in an amount of less than 100 ppm, such as
1 or 2 ppm to 35 or 40 ppm, based on the total weight of all of the
ingredients in the pretreatment composition. The amount of
electropositive metal in the pretreatment composition can range
between the recited values inclusive of the recited values.
In certain embodiments, the pretreatment compositions may also
comprise lithium. In certain embodiments, the source of lithium
used in the pretreatment composition is in the form of a salt.
Suitable lithium salts are lithium nitrate, lithium sulfate,
lithium fluoride, lithium chloride, lithium hydroxide, lithium
carbonate, and lithium iodide.
In certain embodiments, the lithium is present in the pretreatment
composition in an amount of 5 to 500 ppm, such as 25 to 125 ppm,
based on the total weight of the ingredients in the pretreatment
composition. In certain embodiments, the lithium is present in the
pretreatment composition in an amount of less than 200 ppm. The
amount of lithium in the pretreatment composition can range between
the recited values inclusive of the recited values.
In certain embodiments, the pH of the pretreatment composition
ranges from 1 to 6, such as from 2 to 5.5. The pH of the
pretreatment composition may be adjusted using, for example, any
acid or base as is necessary. In certain embodiments, the pH of the
solution is maintained through the inclusion of a basic material,
including water soluble and/or water dispersible bases, such as
sodium hydroxide, sodium carbonate, potassium hydroxide, ammonium
hydroxide, ammonia, and/or amines such as triethylamine,
methylethyl amine, or mixtures thereof.
In certain embodiments, the pretreatment composition also may
comprise a resinous binder. Suitable resins include reaction
products of one or more alkanolamines and an epoxy-functional
material containing at least two epoxy groups, such as those
disclosed in U.S. Pat. No. 5,653,823. In some cases, such resins
contain beta hydroxy ester, imide, or sulfide functionality,
incorporated by using dimethylolpropionic acid, phthalimide, or
mercaptoglycerine as an additional reactant in the preparation of
the resin. Alternatively, the reaction product is that of the
diglycidyl ether of Bisphenol A (commercially available from Shell
Chemical Company as EPON 880), dimethylol propionic acid, and
diethanolamine in a 0.6 to 5.0:0.05 to 5.5:1 mole ratio. Other
suitable resinous binders include water soluble and water
dispersible polyacrylic acids as disclosed in U.S. Pat. Nos.
3,912,548 and 5,328,525; phenol formaldehyde resins as described in
U.S. Pat. No. 5,662,746; water soluble polyamides such as those
disclosed in WO 95/33869; copolymers of maleic or acrylic acid with
allyl ether as described in Canadian patent application 2,087,352;
and water soluble and dispersible resins including epoxy resins,
aminoplasts, phenol-formaldehyde resins, tannins, and polyvinyl
phenols as discussed in U.S. Pat. No. 5,449,415.
In these embodiments of the present invention, the resinous binder
often may be present in the pretreatment composition in an amount
of 0.005 percent to 30 percent by weight, such as 0.5 to 3 percent
by weight, based on the total weight of the ingredients in the
composition.
In other embodiments, however, the pretreatment composition may be
substantially free or, in some cases, completely free of any
resinous binder. As used herein, the term "substantially free",
when used with reference to the absence of resinous binder in the
pretreatment composition, means that any resinous binder is present
in the pretreatment composition in a trace amount of less than
0.005 percent by weight. As used herein, the term "completely free"
means that there is no resinous binder in the pretreatment
composition at all.
The pretreatment composition may optionally contain other materials
such as nonionic surfactants and auxiliaries conventionally used in
the art of pretreatment. In an aqueous medium, water dispersible
organic solvents, for example, alcohols with up to about 8 carbon
atoms such as methanol, isopropanol, and the like, may be present;
or glycol ethers such as the monoalkyl ethers of ethylene glycol,
diethylene glycol, or propylene glycol, and the like. When present,
water dispersible organic solvents are typically used in amounts up
to about ten percent by volume, based on the total volume of
aqueous medium.
Other optional materials include surfactants that function as
defoamers or substrate wetting agents. Anionic, cationic,
amphoteric, and/or nonionic surfactants may be used. Defoaming
surfactants are often present at levels up to 1 weight percent,
such as up to 0.1 percent by weight, and wetting agents are
typically present at levels up to 2 percent, such as up to 0.5
percent by weight, based on the total weight of the pretreatment
composition.
In certain embodiments, the pretreatment composition also may
comprise a silane, such as, for example, an amino group-containing
silane coupling agent, a hydrolysate thereof, or a polymer thereof,
as described in United States Patent Application Publication No.
2004/0163736 A1 at [0025] to [0031], the cited portion of which
being incorporated herein by reference. In other embodiments of the
present invention, however, the pretreatment composition is
substantially free, or, in some cases, completely free of any such
amino group-containing silane coupling agent. As used herein, the
term "substantially free", when used with reference to the absence
of amino-group containing silane coupling agent in the pretreatment
composition, means that any amino-group containing silane coupling
agent, hydrolysate thereof, or polymer thereof that is present in
the pretreatment composition is present in a trace amount of less
than 5 ppm. As used herein, the term "completely free" means that
there is no amino-group containing silane coupling agent,
hydrolysate thereof, or polymer thereof in the pretreatment
composition at all.
In certain embodiments, the pretreatment composition also may
comprise a reaction accelerator, such as nitrite ions, nitro-group
containing compounds, hydroxylamine sulfate, persulfate ions,
sulfite ions, hyposulfite ions, peroxides, iron (III) ions, citric
acid iron compounds, bromate ions, perchlorinate ions, chlorate
ions, chlorite ions as well as ascorbic acid, citric acid, tartaric
acid, malonic acid, succinic acid and salts thereof. Specific
examples of suitable materials and their amounts are described in
United States Patent Application Publication No. 2004/0163736 A1 at
[0032] to [0041], the cited portion of which being incorporated
herein by reference.
In certain embodiments, the pretreatment composition is
substantially or, in some cases, completely free of phosphate ions.
As used herein, the term "substantially free," when used in
reference to the absence of phosphate ions in the pretreatment
composition, means that phosphate ions are not present in the
composition to such an extent that the phosphate ions cause a
burden on the environment. For example, phosphate ions may be
present in the pretreatment composition in a trace amount of less
than 10 ppm. That is, phosphate ions are not substantially used and
the formation of sludge, such as iron phosphate and zinc phosphate,
formed in the case of using a treating agent based on zinc
phosphate, is eliminated.
In certain embodiments, the pretreatment composition also may
include a source of phosphate ions, for example, phosphate ions may
be added in an amount of greater than 10 ppm up to 60 ppm, such as
for example 20 ppm to 40 ppm or for example 30 ppm.
In certain embodiments, the pretreatment composition is
substantially, or in some cases, completely free of chromate. As
used herein, the term "substantially free," when used in reference
to the absence of chromate in the pretreatment composition, means
that any chromate is present in the pretreatment composition in a
trace amount of less than 5 ppm. As used herein, the term
"completely free," when used in reference to the absence of
chromate in the pretreatment composition, means that there is no
chromate in the pretreatment composition at all.
In certain embodiments, the film coverage of the residue of the
pretreatment coating composition generally ranges from 1 to 1000
milligrams per square meter (mg/m.sup.2), for example, from 10 to
400 mg/m.sup.2. In certain embodiments, the thickness of the
pretreatment coating may be less than 1 micrometer, and for example
may be from 1 to 500 nanometers, or from 10 to 300 nanometers.
Following contact with the pretreatment solution, the substrate
optionally may be rinsed with water and dried. In certain
embodiments, the substrate may be dried for 0.5 to 30 minutes in an
oven at 15 to 200.degree. C. (60 to 400.degree. F.), such as for 10
minutes at 70.degree. F.
Optionally, after the pretreatment step, the substrate may then be
contacted with a post-rinse solution. Post-rinse solutions, in
general, utilize certain solubilized metal ions or other inorganic
materials (such as phosphates or simple or complex fluorides) to
enhance the corrosion protection of pretreated metal substrates.
These post-rinse solutions may be chrome containing or non-chrome
containing post-rinse solutions. Suitable non-chrome post-rinse
solutions that may be utilized in the present invention are
disclosed in U.S. Pat. Nos. 5,653,823; 5,209,788; and 5,149,382;
all assigned to PPG Industries, Inc. and herein incorporated by
reference. In addition, organic materials (resinous or otherwise)
such as phosphitized epoxies, base-solubilized, carboxylic acid
containing polymers, at least partially neutralized interpolymers
of hydroxyl-alkyl esters of unsaturated carboxylic acids, and amine
salt-group containing resins (such as acid-solubilized reaction
products of polyepoxides and primary or secondary amines) may also
be utilized alone or in combination with solubilized metal ions
and/or other inorganic materials.
After the optional post-rinse (when utilized), the substrate may be
rinsed with water prior to subsequent processing.
In certain embodiments of the methods of the present invention,
after the substrate is contacted with the pretreatment composition,
it then may be contacted with a coating composition comprising a
film-forming resin. Any suitable technique may be used to contact
the substrate with such a coating composition, including, for
example, brushing, dipping, flow coating, spraying and the like. In
certain embodiments, however, as described in more detail below,
such contacting comprises an electrocoating step wherein an
electrodepositable composition is deposited onto the metal
substrate by electrodeposition.
As used herein, the term "film-forming resin" refers to resins that
can form a self-supporting continuous film on at least a horizontal
surface of a substrate upon removal of any diluents or carriers
present in the composition or upon curing at ambient or elevated
temperature. Conventional film-forming resins that may be used
include, without limitation, those typically used in automotive OEM
coating compositions, automotive refinish coating compositions,
industrial coating compositions, architectural coating
compositions, coil coating compositions, and aerospace coating
compositions, among others.
In certain embodiments, the coating composition comprises a
thermosetting film-forming resin. As used herein, the term
"thermosetting" refers to resins that "set" irreversibly upon
curing or crosslinking, wherein the polymer chains of the polymeric
components are joined together by covalent bonds. This property is
usually associated with a cross-linking reaction of the composition
constituents often induced, for example, by heat or radiation.
Curing or crosslinking reactions also may be carried out under
ambient conditions. Once cured or crosslinked, a thermosetting
resin will not melt upon the application of heat and is insoluble
in solvents. In other embodiments, the coating composition
comprises a thermoplastic film-forming resin. As used herein, the
term "thermoplastic" refers to resins that comprise polymeric
components that are not joined by covalent bonds and thereby can
undergo liquid flow upon heating and are soluble in solvents.
As previously indicated, in certain embodiments, the substrate is
contacted with a coating composition comprising a film-forming
resin by an electrocoating step wherein an electrodepositable
composition is deposited onto the metal substrate by
electrodeposition. In the process of electrodeposition, the metal
substrate being treated, serving as an electrode, and an
electrically conductive counter electrode are placed in contact
with an ionic, electrodepositable composition. Upon passage of an
electric current between the electrode and counter electrode while
they are in contact with the electrodepositable composition, an
adherent film of the electrodepositable composition will deposit in
a substantially continuous manner on the metal substrate.
Electrodeposition is usually carried out at a constant voltage in
the range of from 1 volt to several thousand volts, typically
between 50 and 500 volts. Current density is usually between 1.0
ampere and 15 amperes per square foot (10.8 to 161.5 amperes per
square meter) and tends to decrease quickly during the
electrodeposition process, indicating formation of a continuous
self-insulating film.
The electrodepositable composition utilized in certain embodiments
of the present invention often comprises a resinous phase dispersed
in an aqueous medium wherein the resinous phase comprises: (a) an
active hydrogen group-containing ionic electrodepositable resin,
and (b) a curing agent having functional groups reactive with the
active hydrogen groups of (a).
In certain embodiments, the electrodepositable compositions
utilized in certain embodiments of the present invention contain,
as a main film-forming polymer, an active hydrogen-containing
ionic, often cationic, electrodepositable resin. A wide variety of
electrodepositable film-forming resins are known and can be used in
the present invention so long as the polymers are "water
dispersible," i.e., adapted to be solubilized, dispersed or
emulsified in water. The water dispersible polymer is ionic in
nature, that is, the polymer will contain anionic functional groups
to impart a negative charge or, as is often preferred, cationic
functional groups to impart a positive charge.
Examples of film-forming resins suitable for use in anionic
electrodepositable compositions are base-solubilized, carboxylic
acid containing polymers, such as the reaction product or adduct of
a drying oil or semi-drying fatty acid ester with a dicarboxylic
acid or anhydride; and the reaction product of a fatty acid ester,
unsaturated acid or anhydride and any additional unsaturated
modifying materials which are further reacted with polyol. Also
suitable are the at least partially neutralized interpolymers of
hydroxy-alkyl esters of unsaturated carboxylic acids, unsaturated
carboxylic acid and at least one other ethylenically unsaturated
monomer. Still another suitable electrodepositable film-forming
resin comprises an alkyd-aminoplast vehicle, i.e., a vehicle
containing an alkyd resin and an amine-aldehyde resin. Yet another
anionic electrodepositable resin composition comprises mixed esters
of a resinous polyol, such as is described in U.S. Pat. No.
3,749,657 at col. 9, lines 1 to 75 and col. 10, lines 1 to 13, the
cited portion of which being incorporated herein by reference.
Other acid functional polymers can also be used, such as
phosphatized polyepoxide or phosphatized acrylic polymers as are
known to those skilled in the art.
As aforementioned, it is often desirable that the active
hydrogen-containing ionic electrodepositable resin (a) is cationic
and capable of deposition on a cathode. Examples of such cationic
film-forming resins include amine salt group-containing resins,
such as the acid-solubilized reaction products of polyepoxides and
primary or secondary amines, such as those described in U.S. Pat.
Nos. 3,663,389; 3,984,299; 3,947,338; and 3,947,339. Often, these
amine salt group-containing resins are used in combination with a
blocked isocyanate curing agent. The isocyanate can be fully
blocked, as described in U.S. Pat. No. 3,984,299, or the isocyanate
can be partially blocked and reacted with the resin backbone, such
as is described in U.S. Pat. No. 3,947,338. Also, one-component
compositions as described in U.S. Pat. No. 4,134,866 and DE-OS No.
2,707,405 can be used as the film-forming resin. Besides the
epoxy-amine reaction products, film-forming resins can also be
selected from cationic acrylic resins, such as those described in
U.S. Pat. Nos. 3,455,806 and 3,928,157.
Besides amine salt group-containing resins, quaternary ammonium
salt group-containing resins can also be employed, such as those
formed from reacting an organic polyepoxide with a tertiary amine
salt as described in U.S. Pat. Nos. 3,962,165; 3,975,346; and
4,001,101. Examples of other cationic resins are ternary sulfonium
salt group-containing resins and quaternary phosphonium salt-group
containing resins, such as those described in U.S. Pat. Nos.
3,793,278 and 3,984,922, respectively. Also, film-forming resins
which cure via transesterification, such as described in European
Application No. 12463 can be used. Further, cationic compositions
prepared from Mannich bases, such as described in U.S. Pat. No.
4,134,932, can be used.
In certain embodiments, the resins present in the
electrodepositable composition are positively charged resins which
contain primary and/or secondary amine groups, such as described in
U.S. Pat. Nos. 3,663,389; 3,947,339; and 4,116,900. In U.S. Pat.
No. 3,947,339, a polyketimine derivative of a polyamine, such as
diethylenetriamine or triethylenetetraamine, is reacted with a
polyepoxide. When the reaction product is neutralized with acid and
dispersed in water, free primary amine groups are generated. Also,
equivalent products are formed when polyepoxide is reacted with
excess polyamines, such as diethylenetriamine and
triethylenetetraamine, and the excess polyamine vacuum stripped
from the reaction mixture, as described in U.S. Pat. Nos. 3,663,389
and 4,116,900.
In certain embodiments, the active hydrogen-containing ionic
electrodepositable resin is present in the electrodepositable
composition in an amount of 1 to 60 percent by weight, such as 5 to
25 percent by weight, based on total weight of the
electrodeposition bath.
As indicated, the resinous phase of the electrodepositable
composition often further comprises a curing agent adapted to react
with the active hydrogen groups of the ionic electrodepositable
resin. For example, both blocked organic polyisocyanate and
aminoplast curing agents are suitable for use in the present
invention, although blocked isocyanates are often preferred for
cathodic electrodeposition.
Aminoplast resins, which are often the preferred curing agent for
anionic electrodeposition, are the condensation products of amines
or amides with aldehydes. Examples of suitable amine or amides are
melamine, benzoguanamine, urea and similar compounds. Generally,
the aldehyde employed is formaldehyde, although products can be
made from other aldehydes, such as acetaldehyde and furfural. The
condensation products contain methylol groups or similar alkylol
groups depending on the particular aldehyde employed. Often, these
methylol groups are etherified by reaction with an alcohol, such as
a monohydric alcohol containing from 1 to 4 carbon atoms, such as
methanol, ethanol, isopropanol, and n-butanol. Aminoplast resins
are commercially available from American Cyanamid Co. under the
trademark CYMEL and from Monsanto Chemical Co. under the trademark
RESIMENE.
The aminoplast curing agents are often utilized in conjunction with
the active hydrogen containing anionic electrodepositable resin in
amounts ranging from 5 percent to 60 percent by weight, such as
from 20 percent to 40 percent by weight, the percentages based on
the total weight of the resin solids in the electrodepositable
composition.
As indicated, blocked organic polyisocyanates are often used as the
curing agent in cathodic electrodeposition compositions. The
polyisocyanates can be fully blocked as described in U.S. Pat. No.
3,984,299 at col. 1, lines 1 to 68, col. 2, and col. 3, lines 1 to
15, or partially blocked and reacted with the polymer backbone as
described in U.S. Pat. No. 3,947,338 at col. 2, lines 65 to 68,
col. 3, and col. 4 lines 1 to 30, the cited portions of which being
incorporated herein by reference. By "blocked" is meant that the
isocyanate groups have been reacted with a compound so that the
resultant blocked isocyanate group is stable to active hydrogens at
ambient temperature but reactive with active hydrogens in the film
forming polymer at elevated temperatures usually between 90.degree.
C. and 200.degree. C.
Suitable polyisocyanates include aromatic and aliphatic
polyisocyanates, including cycloaliphatic polyisocyanates and
representative examples include diphenylmethane-4,4'-diisocyanate
(MDI), 2,4- or 2,6-toluene diisocyanate (TDI), including mixtures
thereof, p-phenylene diisocyanate, tetramethylene and hexamethylene
diisocyanates, dicyclohexylmethane-4,4'-diisocyanate, isophorone
diisocyanate, mixtures of phenylmethane-4,4'-diisocyanate and
polymethylene polyphenylisocyanate. Higher polyisocyanates, such as
triisocyanates can be used. An example would include
triphenylmethane-4,4',4''-triisocyanate. Isocyanate ( )-prepolymers
with polyols such as neopentyl glycol and trimethylolpropane and
with polymeric polyols such as polycaprolactone diols and triols
(NCO/OH equivalent ratio greater than 1) can also be used.
The polyisocyanate curing agents are typically utilized in
conjunction with the active hydrogen containing cationic
electrodepositable resin in amounts ranging from 5 percent to 60
percent by weight, such as from 20 percent to 50 percent by weight,
the percentages based on the total weight of the resin solids of
the electrodepositable composition.
In certain embodiments, the coating composition comprising a
film-forming resin also comprises yttrium. In certain embodiments,
yttrium is present in such compositions in an amount from 10 to
10,000 ppm, such as not more than 5,000 ppm, and, in some cases,
not more than 1,000 ppm, of total yttrium (measured as elemental
yttrium).
Both soluble and insoluble yttrium compounds may serve as the
source of yttrium. Examples of yttrium sources suitable for use in
lead-free electrodepositable coating compositions are soluble
organic and inorganic yttrium salts such as yttrium acetate,
yttrium chloride, yttrium formate, yttrium carbonate, yttrium
sulfamate, yttrium lactate and yttrium nitrate. When the yttrium is
to be added to an electrocoat bath as an aqueous solution, yttrium
nitrate, a readily available yttrium compound, is a preferred
yttrium source. Other yttrium compounds suitable for use in
electrodepositable compositions are organic and inorganic yttrium
compounds such as yttrium oxide, yttrium bromide, yttrium
hydroxide, yttrium molybdate, yttrium sulfate, yttrium silicate,
and yttrium oxalate. Organoyttrium complexes and yttrium metal can
also be used. When the yttrium is to be incorporated into an
electrocoat bath as a component in the pigment paste, yttrium oxide
is often the preferred source of yttrium.
The electrodepositable compositions described herein are in the
form of an aqueous dispersion. The term "dispersion" is believed to
be a two-phase transparent, translucent or opaque resinous system
in which the resin is in the dispersed phase and the water is in
the continuous phase. The average particle size of the resinous
phase is generally less than 1.0 and usually less than 0.5 microns,
often less than 0.15 micron.
The concentration of the resinous phase in the aqueous medium is
often at least 1 percent by weight, such as from 2 to 60 percent by
weight, based on total weight of the aqueous dispersion. When such
compositions are in the form of resin concentrates, they generally
have a resin solids content of 20 to 60 percent by weight based on
weight of the aqueous dispersion.
The electrodepositable compositions described herein are often
supplied as two components: (1) a clear resin feed, which includes
generally the active hydrogen-containing ionic electrodepositable
resin, i.e., the main film-forming polymer, the curing agent, and
any additional water-dispersible, non-pigmented components; and (2)
a pigment paste, which generally includes one or more colorants
(described below), a water-dispersible grind resin which can be the
same or different from the main-film forming polymer, and,
optionally, additives such as wetting or dispersing aids.
Electrodeposition bath components (1) and (2) are dispersed in an
aqueous medium which comprises water and, usually, coalescing
solvents.
As aforementioned, besides water, the aqueous medium may contain a
coalescing solvent. Useful coalescing solvents are often
hydrocarbons, alcohols, esters, ethers and ketones. The preferred
coalescing solvents are often alcohols, polyols and ketones.
Specific coalescing solvents include isopropanol, butanol,
2-ethylhexanol, isophorone, 2-methoxypentanone, ethylene and
propylene glycol and the monoethyl monobutyl and monohexyl ethers
of ethylene glycol. The amount of coalescing solvent is generally
between 0.01 and 25 percent, such as from 0.05 to 5 percent by
weight based on total weight of the aqueous medium.
In addition, a colorant and, if desired, various additives such as
surfactants, wetting agents or catalyst can be included in the
coating composition comprising a film-forming resin. As used
herein, the term "colorant" means any substance that imparts color
and/or other opacity and/or other visual effect to the composition.
The colorant can be added to the composition in any suitable form,
such as discrete particles, dispersions, solutions and/or flakes. A
single colorant or a mixture of two or more colorants can be
used.
Example colorants include pigments, dyes and tints, such as those
used in the paint industry and/or listed in the Dry Color
Manufacturers Association (DCMA), as well as special effect
compositions. A colorant may include, for example, a finely divided
solid powder that is insoluble but wettable under the conditions of
use. A colorant can be organic or inorganic and can be agglomerated
or non-agglomerated. Colorants can be incorporated by use of a
grind vehicle, such as an acrylic grind vehicle, the use of which
will be familiar to one skilled in the art.
Example pigments and/or pigment compositions include, but are not
limited to, carbazole dioxazine crude pigment, azo, monoazo,
disazo, naphthol AS, salt type (lakes), benzimidazolone,
condensation, metal complex, isoindolinone, isoindoline and
polycyclic phthalocyanine, quinacridone, perylene, perinone,
diketopyrrolo pyrrole, thioindigo, anthraquinone, indanthrone,
anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone,
dioxazine, triarylcarbonium, quinophthalone pigments, diketo
pyrrolo pyrrole red ("DPPBO red"), titanium dioxide, carbon black
and mixtures thereof. The terms "pigment" and "colored filler" can
be used interchangeably.
Example dyes include, but are not limited to, those that are
solvent and/or aqueous based such as phthalo green or blue, iron
oxide, bismuth vanadate, anthraquinone, perylene, aluminum and
quinacridone.
Example tints include, but are not limited to, pigments dispersed
in water-based or water miscible carriers such as AQUA-CHEM 896
commercially available from Degussa, Inc., CHARISMA COLORANTS and
MAXITONER INDUSTRIAL COLORANTS commercially available from Accurate
Dispersions division of Eastman Chemical, Inc.
As noted above, the colorant can be in the form of a dispersion
including, but not limited to, a nanoparticle dispersion.
Nanoparticle dispersions can include one or more highly dispersed
nanoparticle colorants and/or colorant particles that produce a
desired visible color and/or opacity and/or visual effect.
Nanoparticle dispersions can include colorants such as pigments or
dyes having a particle size of less than 150 nm, such as less than
70 nm, or less than 30 nm. Nanoparticles can be produced by milling
stock organic or inorganic pigments with grinding media having a
particle size of less than 0.5 mm. Example nanoparticle dispersions
and methods for making them are identified in U.S. Pat. No.
6,875,800 B2, which is incorporated herein by reference.
Nanoparticle dispersions can also be produced by crystallization,
precipitation, gas phase condensation, and chemical attrition
(i.e., partial dissolution). In order to minimize re-agglomeration
of nanoparticles within the coating, a dispersion of resin-coated
nanoparticles can be used. As used herein, a "dispersion of
resin-coated nanoparticles" refers to a continuous phase in which
is dispersed discreet "composite microparticles" that comprise a
nanoparticle and a resin coating on the nanoparticle. Example
dispersions of resin-coated nanoparticles and methods for making
them are identified in United States Patent Application Publication
2005-0287348 A1, filed Jun. 24, 2004, U.S. Provisional Application
No. 60/482,167 filed Jun. 24, 2003, and U.S. patent application
Ser. No. 11/337,062, filed Jan. 20, 2006, which is also
incorporated herein by reference.
Example special effect compositions that may be used include
pigments and/or compositions that produce one or more appearance
effects such as reflectance, pearlescence, metallic sheen,
phosphorescence, fluorescence, photochromism, photosensitivity,
thermochromism, goniochromism and/or color-change. Additional
special effect compositions can provide other perceptible
properties, such as opacity or texture. In certain embodiments,
special effect compositions can produce a color shift, such that
the color of the coating changes when the coating is viewed at
different angles. Example color effect compositions are identified
in U.S. Pat. No. 6,894,086, incorporated herein by reference.
Additional color effect compositions can include transparent coated
mica and/or synthetic mica, coated silica, coated alumina, a
transparent liquid crystal pigment, a liquid crystal coating,
and/or any composition wherein interference results from a
refractive index differential within the material and not because
of the refractive index differential between the surface of the
material and the air.
In certain embodiments, a photosensitive composition and/or
photochromic composition, which reversibly alters its color when
exposed to one or more light sources, can be used. Photochromic
and/or photosensitive compositions can be activated by exposure to
radiation of a specified wavelength. When the composition becomes
excited, the molecular structure is changed and the altered
structure exhibits a new color that is different from the original
color of the composition. When the exposure to radiation is
removed, the photochromic and/or photosensitive composition can
return to a state of rest, in which the original color of the
composition returns. In certain embodiments, the photochromic
and/or photosensitive composition can be colorless in a non-excited
state and exhibit a color in an excited state. Full color-change
can appear within milliseconds to several minutes, such as from 20
seconds to 60 seconds. Example photochromic and/or photosensitive
compositions include photochromic dyes.
In certain embodiments, the photosensitive composition and/or
photochromic composition can be associated with and/or at least
partially bound to, such as by covalent bonding, a polymer and/or
polymeric materials of a polymerizable component. In contrast to
some coatings in which the photosensitive composition may migrate
out of the coating and crystallize into the substrate, the
photosensitive composition and/or photochromic composition
associated with and/or at least partially bound to a polymer and/or
polymerizable component in accordance with certain embodiments of
the present invention, have minimal migration out of the coating.
Example photosensitive compositions and/or photochromic
compositions and methods for making them are identified in U.S.
application Ser. No. 10/892,919 filed Jul. 16, 2004, incorporated
herein by reference.
In general, the colorant can be present in the coating composition
in any amount sufficient to impart the desired visual and/or color
effect. The colorant may comprise from 1 to 65 weight percent, such
as from 3 to 40 weight percent or 5 to 35 weight percent, with
weight percent based on the total weight of the composition.
After deposition, the coating is often heated to cure the deposited
composition. The heating or curing operation is often carried out
at a temperature in the range of from 120 to 250.degree. C., such
as from 120 to 190.degree. C., for a period of time ranging from 10
to 60 minutes. In certain embodiments, the thickness of the
resultant film is from 10 to 50 microns.
As will be appreciated by the foregoing description, the present
invention is directed to compositions for treating a metal
substrate. These compositions comprise: a Group IIIB and/or Group
IVB metal; free fluoride; molybdenum; and lithium. The composition,
in certain embodiments, is substantially free of heavy metal
phosphate, such as zinc phosphate and nickel-containing phosphate,
and chromate.
As has been indicated throughout the foregoing description, the
methods and coated substrates of the present invention do not, in
certain embodiments, include the deposition of a crystalline
phosphate, such as zinc phosphate, or a chromate. As a result, the
environmental drawbacks associated with such materials can be
avoided. Nevertheless, the methods of the present invention have
been shown to provide coated substrates that are, in at least some
cases, resistant to corrosion at a level comparable to, in some
cases even superior to, methods wherein such materials are used.
This is a surprising and unexpected discovery of the present
invention and satisfies a long felt need in the art.
Illustrating the invention are the following examples that are not
to be considered as limiting the invention to their details. All
parts and percentages in the examples, as well as throughout the
specification, are by weight unless otherwise indicated.
Example 1
Twelve cold rolled steel (CRS) panels (panels 1-12) were cleaned by
dipping with a solution of Chemkleen 166 M/Chemkleen 171/11, a two
component liquid alkaline cleaner available from PPG Industries,
for three minutes at 60.degree. C. After alkaline cleaning, the
panels were rinsed thoroughly with deionized water then with
deionized water containing 0.25 g/l Zirco Rinse Additive (available
commercially from PPG Industries, Quattordio, Italy).
Six of these panels (panels 1-6) were immersed in a zirconium
pretreatment solution for two minutes at ambient temperature,
designated in Tables 2-3 as "Pretreatment A." Pretreatment A was
prepared by diluting 4.5 liters Zircobond ZC (a hexafluorozirconic
acid copper containing agent available commercially from PPG
Industries, Quattordio, Italy) with approximately 400 liters of
deionized water to a zirconium concentration of 175 ppm (as
zirconium) and adjusting the pH to 4.5 with Chemfill Buffer/M (a
mild alkaline buffering agent available commercially from PPG
Industries, Quattordio, Italy).
After pretreatment in a solution of Pretreatment A, panels 1-6 were
rinsed with deionized water containing 0.25 g/1 Zirco Rinse
Additive then were thoroughly rinsed with deionized water, and then
were dried for 10 minutes in an oven at 70.degree. C. Panels 1-6
had a light bronze appearance and the coating thickness was
measured using a portable X-ray Fluorescence instrument (XRF) at
approximately 39 nm.
The pretreatment solution referred to in Table 2 as "Pretreatment
B" was prepared by adding 40 g of sodium molybdate dihydrate
(available from Sigma Aldrich code 71756) to Pretreatment A
solution in order to obtain a concentration of 40 ppm molybdenum.
Panels 7-12 were then immersed in Pretreatment B solution for two
minutes at ambient temperature. After pretreatment in Pretreatment
B solution, panels 7-12 were rinsed with deionized water containing
0.25 g/1 Zirco Rinse Additive, then were rinsed thoroughly with
deionized water and were then dried for 10 minutes in an oven at
70.degree. C. Panels 7-12 had a bronze appearance with some blue
iridescence and the coating thickness as measured by XRF was
approximately 35 nm.
Each of the panels, i.e., panels 1-6 pretreated with Pretreatment A
and panels 7-12 pretreated with Pretreatment B, were then coated
with G6MC3, a yttrium-containing cathodic electrocoat commercially
available from PPG Industries that contains 422 g of resin (W7827
commercially available from PPG Industries, Inc.), 98 g of paste
(P9757, commercially available from PPG Industries, Inc.), and 480
g of water. The G6MC3 coating bath was prepared and coated
according to the manufacturer's instructions. The panels were cured
according to the manufacturer's specifications.
After curing, three of the coated panels pretreated with
Pretreatment A and three of the coated panels pretreated with
Pretreatment B were subjected to a VW cyclic corrosion test PV1210.
After a scribe and a first stone chipping, the three coated panels
pretreated with Pretreatment A and the three panels pretreated with
Pretreatment B were exposed to condensing humidity (4 hours NSS at
35.degree. C. then 4 hours at 23.degree. C. and 50% humidity
followed by 16 hours at 40.degree. C. and 100% humidity) for 30
days, and then a second PV1210 test was run on the exposed panels.
The stone chipping results were rated on a scale of 0 to 5, where 5
indicates complete paint loss, and 0 indicates perfect paint
adhesion. After humidity exposure, the corrosion creepage along the
scribe and stone chipping results were measured.
The remaining three coated panels pretreated with Pretreatment A
and the remaining three coated panels pretreated with Pretreatment
B were subjected to a GM cyclic corrosion test GMW14872 in which
the panels were scratched by cutting through the coating system
down to metal. The panels were exposed to condensing humidity (8
hours at 25.degree. C. and 45% humidity then 8 hours at 49.degree.
C. and 100% humidity followed by 8 hours at 60.degree. C. and 30%
humidity) for 40 days. At the end of the test, the panels were
rated by measuring the paint loss from the scribe (creep) and the
maximum creepage (both sides) calculated in millimeters for each
panel. Results are summarized in Table 2 below.
The pretreatment film was tested using Time-of-Flight Secondary Ion
Mass Spectrometry (ToF-SIMS), which indicated that the film was
crystalline and that zirconium, oxygen, fluoride, and molybdenum
were present in the film. Molybdenum was present throughout the
coating as mixed molybdenum oxides. X-Ray Photoelectron
Spectroscopy (XPS) and X-Ray Fluorescence Spectroscopy (XRF)
confirmed the presence of molybdenum in the zirconium oxide film
1-10% of the zirconium oxide film weight.
TABLE-US-00002 TABLE 2 30 cycles VW PV1210 test 40 cycles GMW
Corrosion Stone 14872 test along the chipping Pretreat- Corrosion
along scribe creepage ment Electrocoat the scribe (mm) (mm) rating
A G6MC3 9.5 1.2 4.0 B G6MC3 5.0 0.5 2.5
Example 2
Cold rolled steel panels were pretreated as in Example 1, with half
of the panels being pretreated with Pretreatment A and the other
half being pretreated with "Pretreatment C," where Pretreatment C
was prepared by adding lithium nitrate and sodium molybdate to
Pretreatment A in order to obtain a concentration of 40 ppm
molybdenum and 100 ppm lithium. Each panel was dried by placing it
in an oven at 70.degree. C. for approximately ten minutes. The
coating thickness as measured by XRF was approximately 40 nm.
The panels were subsequently electrocoated with one
yttrium-containing electrocoat ED6070/2, a yttrium-containing
cathodic electrocoat commercially available from PPG Industries
that contains 472 g of resin (W7910, commercially available from
PPG Industries, Inc.), 80 g of paste (P9711, commercially available
from PPG Industries, Inc.), and 448 g of water. The panels were
subjected to the VW cyclic corrosion test PV1210. The results
appear in Table 3 below.
The film on the panels pretreated with Pretreatment C was tested
using ToF-SIMS, XPS, and XRF. ToF-SIMS indicated the presence of
lithium and molybdenum throughout the coating and that molybdenum
was present in the mixed oxide form. XPS and XRF confirmed the
presence of molybdenum at 1-10% of the zirconium oxide film weight.
Zirconium, oxygen, fluoride, lithium, and molybdenum were present
in the film.
TABLE-US-00003 TABLE 3 30 cycles VW PV1210 test Corrosion along
Stone chipping Pretreatment Electrocoat the scribe (mm) creepage
rating A ED6070/2 0.75 2.5 C ED6070/2 0.5 2
Example 3
Cold rolled steel panels were pretreated as in Example 1, with six
of the panels being pretreated with Pretreatment A and six of the
panels being treated with "Pretreatment D," where Pretreatment D
was prepared by adding sodium molybdate to Pretreatment A in order
to obtain a concentration of 40 ppm molybdenum. Each panel was
dried by placing it in an oven at 70.degree. C. for approximately
ten minutes. The coating thickness as measured by XRF was
approximately 40 nm.
The panels were subsequently electrocoated with electrocoat ED7000P
a cathodic electrocoat commercially available from PPG Industries,
with or without the addition of 2.4 g of yttrium sulfamate (10%
w/w). EDP7000P is a cathodic electrocoat available from PPG
Industries that contains 509 g of resin (E6433, commercially
available from PPG Industries, Inc.), 86 g of paste (E6434P,
commercially available from PPG Industries, Inc.), and 404 g water.
The panels were subjected to a GMW14872 TEST (10 year equivalent).
Results are shown in Table 4.
The results in Table 4 suggest that the addition of yttrium to
electrocoat has a negative effect on corrosion on Pretreatment A
solution. However, the corrosion performance is improved in panels
having a yttrium-containing electrocoat and pretreated with
Pretreatment D, which contains molybdenum.
TABLE-US-00004 TABLE 4 10 Year Equivalent GMW14872 Corrosion along
the scribe (maximum left + Pretreatment Electrocoat maximum right)
mm A ED7000P 5.8 A ED7000P + 200 ppm Y 8.6 D ED7000P 7.9 D ED7000P
+ 200 ppm Y 5.9
It will be appreciated by those skilled in the art that changes
could be made to the embodiments described above without departing
from the broad inventive concept thereof. It is understood,
therefore, that this invention is not limited to the particular
embodiments disclosed, but it is intended to cover modifications
which are within the spirit and scope of the invention, as defined
by the appended claims.
* * * * *